
package main

import (
	"fmt"
	"math"
	"net/http"
	"log"
)

const (
	width, height = 600, 320
	cells = 100
	xyrange = 30.0
	xyscale = width / 2/ xyrange
	zscale = height * 0.4
	angle = math.Pi / 6
)

var sin30, cos30 = math.Sin(angle), math.Cos(angle) // // sin(30°), cos(30°)

func main() {
	http.HandleFunc("/", handler)
	log.Fatal(http.ListenAndServe("localhost:8000", nil))
}

func handler(w http.ResponseWriter, r *http.Request){
	w.Header().Set("Content-Type", "image/svg+xml")
	var src = fmt.Sprintf("<svg xmlns='http://www.w3.org/2000/svg' "+
		"style='stroke: grey; fill: white; stroke-width: 0.7' "+
		"width='%d' height='%d'>", width, height)
		for i := 0; i < cells; i++ {
			for j := 0; j< cells; j++ {
				ax, ay := corner(i+1, j)
				bx, by := corner(i, j)
				cx, cy := corner(i, j+1)
				dx, dy := corner(i+1, j+1)
				src += fmt.Sprintf("<polygon points='%g,%g %g,%g %g,%g %g,%g'/>\n", ax, ay, bx, by, cx, cy, dx, dy)
			}
		}
	src += fmt.Sprintf("</svg>")
	fmt.Fprintf(w, src)

}


func corner(i, j int) (float64, float64) {
	x := xyrange * (float64(i)/cells - 0.5)
	y := xyrange * (float64(j)/cells - 0.5)
	
	z := f(x, y)
	
	sx := width/2 + (x-y)*cos30*xyscale
	sy := height/2 + (x+y)*sin30*xyscale - z*zscale
	return sx, sy
}

func f(x, y float64) float64 {
	r := math.Hypot(x, y) // distance from (0,0)
	return math.Sin(r) /r
}